1. Field of the Invention
The present invention relates to a stepping motor control circuit and an analog electronic timepiece using the stepping motor control circuit.
2. Description of the Related Art
In a background art, there is used a stepping motor including a stator having a rotor containing hole and a positioning portion of determining a position of stopping a rotor, the rotor arranged at inside of the rotor containing hole, and a coil for rotating the rotor by generating a magnetic flux at the stator by supplying an alternating signal to the coil and stopping the rotor at a position in correspondence with the positioning portion in an analog electronic timepiece or the like.
As in inventions described in Patent References JP-B-63-018148, JP-B-63-018149 and JP-B-57-018440, an electronic timepiece mounted with a stepping motor control circuit which is driven by a minimum energy of a background art is constituted to drive a stepping motor by a plurality of kinds of drive pulses. By receiving a detection result of a rotation detecting circuit of detecting a situation of rotating the stepping motor, when the stepping motor is not rotated, a main drive pulse is changed to a main drive pulse having a larger energy (referred to as pulse up or rank up), and the operation is repeated until reaching a drivable main drive pulse. Further, at each constant period of time, a main drive pulse is changed to a main drive pulse having a smaller energy (referred to as pulse down or rank down), and it is confirmed whether the pulse up is carried out excessively. A drive allowance of the stepping motor can be determined at time of detecting an induced voltage (detecting signal) exceeding a predetermined reference threshold voltage, and therefore, when it is determined that there is not the drive allowance, the pulse down is prohibited.
By carrying out the driving operation alternately by using drive pulses of two polarities, stable driving is made to be realized while achieving low power consumption formation.
However, in a case in which although there is the drive allowance on one polarity side, there is not the drive allowance on other polarity side by variations of a stepping motor, when a period of pulse down is made to be in conformity with the polarity having the drive allowance, the pulse down is carried out in conformity with the polarity having the drive allowance. In this case, in successive driving, a combination of the polarity which is not provided with the drive allowance and the main drive pulse after pulse down is constituted, and therefore, a problem of bringing about nonrotation is posed.
Further, when a state in which there is not the drive allowance by variations in a train wheel load continues and a timing at which it is rarely determined that there is the drive allowance and the period of pulse down are overlapped, a problem of bringing about nonrotation in successive driving is posed.